This invention relates to the separation of materials and in particular, to new and improved methods and apparatus suitable for separation of isotopes of heavy metal in relatively large quantities at relatively low cost.
An important use for methods and apparatus of this type is in the production of uranium 235 by separation of uranium 235 from its isotope uranium 238. The methods and apparatus are sometimes used in the separation of uranium 235 from a mixture of the isotopes, and sometimes in the enrichment of such a mixture by increasing the percentage of uranium 235 present in the mixture. A number of techniques have been considered and/or utilized in the separation of isotopes of heavy metals, including gaseous diffusion, centrifuge enriching, and laser isotope separation.
In all uranium enrichment techniques being pursued the problem is that .sup.235 U and .sup.238 U differ little in mass. They do not easily lend themselves to separation by mass differences in gaseous diffusion unless catalysts are introduced and then separated by distillation. This process of catalyst addition and then separation adds expense. Gaseous diffusion, an inherently inefficient process, requires a large volume facility and this is very expensive. The laser separation technique takes advantage of the difference between the excitation levels of .sup.235 U and .sup.238 U by using a laser to excite .sup.235 U to a level so that it can be easily ionized with further radiation or preferentially reacted with a catalyst. Problems with this process involve the need for an atomic vapor which requires a high temperature corrosion resistant system. Also needed is a high power laser for large scale operation and this is an inherently low efficiency operation. If catalysts are used, the separating cost is an additional expense. Laser separation is also critically dependent upon spectral absorption cross section of .sup.235 U which is uncertain. The centrifuge enrichment process requires development of new materials for the high temperature operation and reliability needed for efficient operation. Multistage processing has to be demonstrated to prove feasibility.
An electromagnetic type of separation is shown in U.S. Pat. No. 2,709,222 which describes a "calutron" developed by Dr. Ernest O. Lawrence. In this instrument, a gas such as UCl.sub.4 or UF.sub.6 is fed into an electric arc chamber where the gas is ionized by electron bombardment to form a plasma. Ions are extracted from this plasma through a slit and accelerated by a high voltage electrode. The ion current is limited by the width of the slit and the applied voltage. This ion source is installed in an evacuated container positioned between the poles of an electromagnet. The ions emerging from the source travel in circular orbits through an angle of 180.degree. to collectors also within the magnetic field. Since the ions of the isotopes have slightly different masses, the orbital radii for the isotopes will be different permitting separation at the collectors provided that the orbital radii are sufficiently large such that the dispersion is greater than the beam spread at the collector surface.
While some of the prior art processes have been utilized in the separation of isotopes and theoretically all of them can be used, they all have disadvantages which cause them to be relatively expensive and relatively inefficient.
Accordingly, it is an object of the present invention to provide a new and improved method and apparatus for separation of materials which does not require chemical additives such as catalysts nor excitation by photons such as from a laser nor any mechanical motion. A further object is to provide a new and improved electromagnetic separation system utilizing an efficient ion source capable of producing large currents from a very narrow liquid surface rather than a relatively broad plasma surface. A particular object is to provide such a separator which is small and economical to construct relative to present separators and which requires less power to operate.